Similar to Corion's suggestion:

While generating the form, include hidden fields containing the md5 (or smaller-sized) checksums for the "sent" content of each field.

On return, compare the checksum with the received content, and act accordingly.

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In reply to Re: How to get only changed parameter names from CGI script on form submit? by NetWallah
in thread [Solved]: How to get only changed parameter names from CGI script on form submit? by Perl300

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